U.S. patent application number 11/306207 was filed with the patent office on 2006-09-07 for acceleration sensor.
This patent application is currently assigned to OKI ELECTRIC INDUSTRY CO., LTD.. Invention is credited to Yoshihiko Ino.
Application Number | 20060196270 11/306207 |
Document ID | / |
Family ID | 36671868 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060196270 |
Kind Code |
A1 |
Ino; Yoshihiko |
September 7, 2006 |
Acceleration sensor
Abstract
An acceleration sensor has a semiconductor acceleration sensor
chip and a case. The semiconductor acceleration sensor chip has a
fixed portion, a plummet portion surrounding the fixed portion
without contacting the fixed portion, and a beam portion connecting
the fixed portion and the plummet portion, the thickness of the
beam portion being thinner than the thickness of the fixed portion.
The case has a cavity housing the semiconductor acceleration sensor
chip, and a projection portion formed on the bottom face of the
cavity, the bottom face of the fixed portion being fixed to the top
face of the projection portion.
Inventors: |
Ino; Yoshihiko; (Miyazaki,
JP) |
Correspondence
Address: |
GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Assignee: |
OKI ELECTRIC INDUSTRY CO.,
LTD.
7-12, Toranomon 1-chome, Minato-ku
Tokyo
JP
|
Family ID: |
36671868 |
Appl. No.: |
11/306207 |
Filed: |
December 20, 2005 |
Current U.S.
Class: |
73/514.16 |
Current CPC
Class: |
H01L 2224/48227
20130101; G01P 2015/084 20130101; H01L 2924/1461 20130101; H01L
2924/00 20130101; H01L 2224/48227 20130101; H01L 2924/00014
20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L
2224/45144 20130101; H01L 2224/48091 20130101; G01P 1/023 20130101;
G01P 15/123 20130101; G01P 15/18 20130101; H01L 2924/1461 20130101;
H01L 2224/48137 20130101; H01L 2224/49171 20130101; H01L 2224/49171
20130101; H01L 2224/48091 20130101; H01L 2224/45144 20130101 |
Class at
Publication: |
073/514.16 |
International
Class: |
G01P 15/00 20060101
G01P015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2004 |
JP |
2004-367933 |
Claims
1. An acceleration sensor comprising: a semiconductor acceleration
sensor chip having a fixed portion, a plummet portion surrounding
the fixed portion without contacting the fixed portion, and a beam
portion connecting the fixed portion and the plummet portion, the
thickness of the beam portion being thinner than the thickness of
the fixed portion; and a case having a cavity housing the
semiconductor acceleration sensor chip, and a projection portion
formed on a bottom face of the cavity, a bottom face of the fixed
portion being fixed to a top face of the projection portion.
2. The acceleration sensor according to claim 1, wherein the shape
of the plummet portion is an approximately square column which has
a cavity for housing the fixed portion in the center thereof, and
the beam portion connects the plummet portion and the fixed portion
on the diagonal line of the cavity of the plummet portion.
3. The acceleration sensor according to claim 2, further
comprising: first electrodes formed on the surface of the fixed
portion at predetermined intervals.
4. The acceleration sensor according to claim 3, further
comprising: external wiring electrodes formed at one or more side
faces of the case, the external wiring electrodes being
electrically led to the exterior of the case; and bonding wires
electrically connecting the first electrodes and the external
wiring electrodes.
5. The acceleration sensor according to claim 3, wherein the
bonding wire is a gold wire and bonded to the first electrode and
the external wiring electrode by means of an ultrasonic concomitant
thermocompression bonding method.
6. The acceleration sensor according to claim 4, wherein the shape
of the fixed portion is an approximately square column.
7. The acceleration sensor according to claim 6, wherein the shape
of the projection portion is an approximately square column.
8. The acceleration sensor according to claim 7, wherein the case
is comprised of a ceramic material, and the projection portion is
formed by attaching an approximately square green sheet to the
surface of another green sheet which is to become the bottom face
of the cavity of the case, and sintering the same.
9. The acceleration sensor according to claim 7, wherein the case
is comprised of a ceramic material, and the projection portions are
formed by attaching an approximately square resin film to the
bottom face of the cavity of the case.
10. The acceleration sensor according to claim 4, wherein the shape
of the fixed portion is an approximately circular cylinder.
11. The acceleration sensor according to claim 10, wherein the
shape of the projection portion is an approximately circular
cylinder.
12. The acceleration sensor according to claim 11, wherein the case
is comprised of a ceramic material, and the projection portion is
formed by attaching an approximately circular green sheet to the
surface of another green sheet which is to become the bottom face
of the cavity of the case, and sintering the same.
13. The acceleration sensor according to claim 11, wherein the case
is comprised of a ceramic material, and the projection portion is
formed by attaching an approximately circular resin film to the
bottom face of the cavity of the case.
14. The acceleration sensor according to claim 1, further
comprising: an integrated circuit fixed on the bottom face of the
cavity of the case, the integrated circuit connected with the
semiconductor acceleration sensor chip.
15. The acceleration sensor according to claim 14, wherein the
shape of the plummet portion is an approximately square column
which has a cavity for housing the fixed portion in the center
thereof, and the beam portion connects the plummet portion and the
fixed portion on the diagonal line of the cavity of the plummet
portion.
16. The acceleration sensor according to claim 15, further
comprising: first electrodes formed on the surface of the fixed
portion at predetermined intervals.
17. The acceleration sensor according to claim 16, further
comprising: second electrodes formed on the surface of the
integrated circuit at predetermined intervals.
18. The acceleration sensor according to claim 17, further
comprising: bonding wires electrically connecting the first
electrodes and the second electrodes.
19. The acceleration sensor according to claim 18, wherein the
bonding wire is a gold wire and bonded to the first electrode and
the second electrode by mean of an ultrasonic concomitant
thermocompression bonding method.
20. The acceleration sensor according to claim 18, further
comprising: external wiring electrodes formed at one or more side
faces of the case, the external wiring electrodes being
electrically led to the exterior of the case; and bonding wires
that respectively electrically connect the first electrodes and the
external wiring electrodes, and the second electrodes and the
external wiring electrode.
21. The acceleration sensor according to claim 20, wherein the
bonding wire is a gold wire and bonded to the first electrode and
the external wiring electrode by means of an ultrasonic concomitant
thermocompression bonding method.
22. The acceleration sensor according to claim 20, wherein the
shape of the fixed portion is an approximately square column.
23. The acceleration sensor according to claim 22, wherein the
shape of the projection portion is an approximately square
column.
24. The acceleration sensor according to claim 23, wherein the case
is comprised of a ceramic material, and the projection portion is
formed by attaching an approximately square green sheet to the
surface of another green sheet which is to become the bottom face
of the cavity of the case, and sintering the same.
25. The acceleration sensor according to claim 23, wherein the case
is comprised of a ceramic material, and the projection portions are
formed by attaching an approximately square resin film to the
bottom face of the cavity of the case.
26. The acceleration sensor according to claim 20, wherein the
shape of the fixed portion is an approximately circular
cylinder.
27. The acceleration sensor according to claim 26, wherein the
shape of the projection portion is an approximately circular
cylinder.
28. The acceleration sensor according to claim 27, wherein the case
is comprised of a ceramic material, and the projection portion is
formed by attaching an approximately circular green sheet to the
surface of another green sheet which is to become the bottom face
of the cavity of the case, and sintering the same.
29. The acceleration sensor according to claim 27, wherein the case
is comprised of a ceramic material, and the projection portion is
formed by attaching an approximately circular resin film to the
bottom face of the cavity of the case.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an acceleration sensor,
which in particular is capable of detecting accelerations acting
upon three axes, respectively.
[0003] 2. Background Information
[0004] In recent years, acceleration sensors are widely used in all
kinds of precision instruments, cars, robots and other various
industrial fields. Especially, there is an increasing demand for a
semiconductor acceleration sensor, which uses an MEMS (micro
electro mechanical system) technology, as it is small in size,
light, accurate and reliable in operation, and available at low
cost.
[0005] In most semiconductor acceleration sensors, the
piezoresistance effect, i.e. a phenomenon in which an electric
resistivity changes in proportion to stress, is used in detecting
acceleration. A common semiconductor acceleration sensor, for
instance, is formed by having a semiconductor acceleration sensor
chip fixed on a pedestal of a ceramic substrate forming a portion
of a package. This semiconductor acceleration sensor chip has a
plummet disposed in a central portion of the semiconductor
acceleration sensor chip and four flexible beams which hang the
plummet such that the beams will bend in response to the
accelerations acting on the plummets. The four flexible beams and
the plummet are formed by processing one semiconductor substrate.
On the surfaces of the four flexible beams, piezo elements are
formed, respectively, and these piezo elements constitute a
Wheatstone bridge circuit. When stress occurs at the beam by the
act of acceleration, the resistance balance of the Wheatstone
bridge will change, and the acceleration is detected by having this
resistance change measured as a current change or a voltage
change.
[0006] For example, inventions relating to the acceleration sensor
are disclosed in Japanese Patent No. 2127840, p. 11, FIG. 11
(hereinafter to be referred to as Patent Reference 1), Japanese
Laid Open Patent Application No. 9-61448, pp. 2-3, FIG. 3
(hereinafter to be referred to as Patent Reference 2) and Japanese
Laid Open Patent Application No. 10-123166, pp. 5-8, FIGS. 1-6
(hereinafter to be referred to as Patent Reference 3).
[0007] The invention disclosed in Patent Reference 1 relates to a
semiconductor acceleration sensor using piezo elements, and it has
an acting unit (a plummet portion) in a peripheral portion of a
silicon monocrystal substrate that performs the main functions of
the semiconductor acceleration sensor, flexible portions (beam
portions) inside the acting unit, and a fixed portion in a central
portion of this silicon monocrystal substrate. The monocrystal
substrate is fixed directly to the bottom face of the package
through the conical pedestal disposed on the under surface of the
fixed portion. When a cylindrical plumb disposed on the under
surface of the acting portion (plummet portion) is displaced due to
acceleration, this displacement is transmitted to the flexible
portions (beam portions) of the monocrystal substrate, and stress
accrues on piezo elements formed on the flexible portions. Thereby,
the acceleration applied to the semiconductor acceleration sensor
is detected. With this semiconductor acceleration sensor structure,
the displacement of the plumb in the right and left directions is
made to stay within a predetermined limit by a gap formed between
the plumb and the pedestal.
[0008] The invention disclosed in Patent Reference 2 relates to an
acceleration sensor using piezoelectric ceramics. With respect to
the invention disclosed in Patent Reference 2, in mounting the
acceleration sensor of which one end is closed on a circuit
substrate, an integrated circuit for sensor driving is disposed in
between the acceleration sensor and the circuit substrate. Due to
such arrangement, the mounting area for the acceleration sensor can
be minimized, the circuit pattern of the circuit substrate can be
shortened, and noise resistance can be improved.
[0009] The invention disclosed in Patent Reference 3 relates to a
semiconductor acceleration sensor using a piezo element. With
respect to the invention disclosed in Patent Reference 3, a
semiconductor acceleration sensor chip having a plummet portion
hung by beam portions is fixed on a pedestal which is formed by a
material having the same thermal expansion coefficient as the
semiconductor acceleration sensor, and the pedestal and the plummet
portion are disposed closely such that an air gap between the two
stays within a range of 7 to 15 .mu.z. With this semiconductor
acceleration sensor structure, it is possible to damp the
vibrations of the plummet portion by means of air damping between
the plummet portion and the pedestal, and stabilize the output
characteristic of the sensor, by which a comparatively low level of
acceleration can be detected.
[0010] In order to minimize the size of the semiconductor
acceleration sensor, it is necessary to minimize and reduce the
thickness of the plummet portion. Normally, when the plummet
portion is minimized or made thinner, the moment of inertia becomes
smaller, which desensitizes the acceleration sensor. Therefore, in
this case, it is also necessary to reduce the thickness of the
flexible beam portion in order to raise the sensitivity of the
acceleration sensor. However, making the beam portion thinner
deteriorates the shock-resistance of the semiconductor acceleration
sensor, and the semiconductor acceleration sensor may become
vulnerable to external shocks, such as shocks caused by dropping.
Moreover, when the beam portion is made thinner, the semiconductor
acceleration sensor may be damaged by receiving shocks in its
manufacturing process, which can result in a reduction in the yield
ratio. For instance, the semiconductor acceleration sensor may be
damaged by water pressure during the dicing process or by force
that can be applied to it during pick up. Considering these
problems, a semiconductor acceleration sensor which can have a
small size and thin configuration, and which can have improved
shock-resistance, is required.
[0011] In the acceleration sensor of Patent Reference 1, the fixed
portion is formed in the central portion of the silicon monocrystal
substrate, and the monocrystal substrate is fixed directly to the
bottom face of the package through the conical pedestal disposed on
the under surface of the fixed portion. Therefore, it is necessary
to have a process of forming a gap between the under surface level
of the cylindrical plumb disposed on the under surface of the
acting unit (plummet portion) in the peripheral portion, and the
under surface level of the conical pedestal disposed on the under
surface of the fixed portion. It is a problem because such process
may complicate the overall manufacturing process. In addition,
Patent Reference 1 does not make any reference to the
shock-resistance of the acceleration sensor, especially the
shock-resistance of the beam portion.
[0012] In the acceleration sensor of Patent Reference 2, a plummet
portion is disposed in a central portion of the bottom-bearing
cylindrical acceleration sensor to which piezoelectric ceramics are
used as its material. Therefore, in order to minimize the size of
the acceleration sensor, it is necessary to minimize and reduce the
thickness of the plummet portion and to reduce the thickness of the
flexible portions having sensor functions at the same time.
Accordingly, it is a problem because the shock-resistance of the
acceleration sensor may be deteriorated due to such arrangement,
and the acceleration sensor may become vulnerable to external
shocks.
[0013] In the acceleration sensor of Patent Reference 3, the
plummet portion is formed in a central portion of a semiconductor
substrate, and it is supported by a frame body in a peripheral
portion through the flexible beam portion. Therefore, in order to
minimize the size of the acceleration sensor, it is necessary to
minimize and reduce the thickness of the plummet portion and to
reduce the thickness of the flexible beam portion at the same time.
Accordingly, it is a problem because the shock-resistance of the
acceleration sensor may be deteriorated due to such arrangement,
and the acceleration sensor may become vulnerable to external
shocks.
[0014] In view of the above, it will be apparent to those skilled
in the art from this disclosure that there exists a need for an
improved acceleration sensor. This invention addresses this need in
the art as well as other needs, which will become apparent to those
skilled in the art from this disclosure.
SUMMARY OF THE INVENTION
[0015] It is therefore an object of the present invention to
resolve the above-described problems, and to provide an
acceleration sensor which can have a small size and thin
configuration, and which can have improved shock-resistance.
[0016] In accordance with one aspect of the present invention, an
acceleration sensor has a semiconductor acceleration sensor chip
and a case. The semiconductor acceleration sensor chip has a fixed
portion, a plummet portion surrounding the fixed portion without
contacting the fixed portion, and a beam portion connecting the
fixed portion and the plummet portion, the thickness of the beam
portion being thinner than the thickness of the fixed portion. The
case has a cavity housing the semiconductor acceleration sensor
chip, and a projection portion formed on the bottom face of the
cavity, the bottom face of the fixed portion being fixed to the top
face of the projection portion.
[0017] In accordance with another aspect of the present invention,
an acceleration sensor has a semiconductor acceleration sensor
chip, an integrated circuit and a case. The semiconductor
acceleration sensor chip has a fixed portion, a plummet portion
surrounding the fixed portion without contacting the fixed portion,
and a beam portion connecting the fixed portion and the plummet
portion, the thickness of the beam portion being thinner than the
thickness of the fixed portion. The integrated circuit is fixed to
the bottom face of the semiconductor acceleration sensor chip. The
case has a cavity housing the semiconductor acceleration sensor
chip and the integrated circuit, the bottom face of the integrated
circuit being fixed to the bottom face of the cavity of the
case.
[0018] These and other objects, features, aspects, and advantages
of the present invention will become apparent to those skilled in
the art from the following detailed description, which, taken in
conjunction with the annexed drawings, discloses preferred
embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Referring now to the attached drawings which form a part of
this original disclosure:
[0020] FIG. 1A and FIG. 1B are diagrams showing the structure of a
semiconductor acceleration sensor according to a first embodiment
of the present invention;
[0021] FIG. 2A and FIG. 2B are diagrams showing the structure of a
semiconductor acceleration sensor according to a second embodiment
of the present invention;
[0022] FIG. 3 is a comparative diagram showing the difference in
the joint areas between a fixed portion in the first embodiment and
a fixed portion in the second embodiment;
[0023] FIG. 4A and FIG. 4B are diagrams showing the structure of a
semiconductor acceleration sensor according to a third embodiment
of the present invention; and
[0024] FIG. 5A and FIG. 5B are diagrams showing the structure of a
semiconductor acceleration sensor according to a fourth embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Selected embodiments of the present invention will now be
explained with reference to the drawings. It will be apparent to
those skilled in the art from this disclosure that the following
descriptions of the embodiments of the present invention are
provided for illustration only and not for the purpose of limiting
the invention as defined by the appended claims and their
equivalents.
First Embodiment
[0026] FIG. 1A and FIG. 1B are diagrams showing the structure of a
semiconductor acceleration sensor 100 according to a first
embodiment of the present invention. FIG. 1A is a plan view of the
semiconductor acceleration sensor 100 when it is viewed from above,
and FIG. 1B is a sectional view of the semiconductor acceleration
sensor 100 taken along a line A-A' shown in FIG. 1A. Note that for
convenience of explanation, FIG. 1A shows a state in which the
cover 55, which is supposed to be placed on the upper surface of
the semiconductor acceleration sensor 100, is removed.
[0027] The semiconductor acceleration sensor 100 has a
semiconductor acceleration sensor chip 10 housed in a case 50 and
it is hermetically sealed by a cover 55.
[0028] The semiconductor acceleration sensor chip 10 is formed
using a silicon semiconductor substrate, for instance, and it has a
fixed portion 11, a plummet portion 12 and beam portions 13.
[0029] The fixed portion 11 is placed at a central portion of the
semiconductor acceleration sensor chip 10, and it has a square
column structure in which the shape thereof when viewed from above
is an approximate square. A plurality of electrode pads 15 (which
will be described later on) are disposed on the upper surface of
the fixed portion 11 at predetermined intervals. The electrode pads
15 serve to take out signals from piezo elements 16 (which will be
described later on) to the outside. The under surface of the fixed
portion 11 is fixed on a projection portion 51a which is formed on
a bottom face portion 51 of the case 50 (which will be described
later on).
[0030] The plummet portion 12 is a frame like portion shaped in an
approximate square, and it is located in a peripheral portion of
the semiconductor acceleration sensor chip 10 and formed in a way
which surrounds the fixed portion 11. By having the plummet portion
12 disposed in the peripheral portion of the semiconductor
acceleration sensor chip 10, it is possible to set the volume of
the plummet portion to be larger than the structure of the
conventional semiconductor sensor chip, i.e. the structure in which
the plummet portion is placed at a central portion of the
semiconductor acceleration sensor chip. Thereby, even if the
overall structure of the semiconductor acceleration sensor chip is
made thinner, a predetermined moment of inertia will act, and it
will be possible to prevent the sensitivity of the acceleration
sensor from deteriorating. Moreover, the under surface of the fixed
portion 11 and the under surface of the plummet portion 12 are
formed at approximately the same height. This means that the
manufacturing process of the semiconductor acceleration sensor chip
10 can be simplified. To be more precise, with respect to the
structure of the conventional semiconductor acceleration sensor
chip, a gap has to be formed between the under surface of the
plummet portion and the under surface of the fixed portion in order
to let the plummet portion displace more freely in response to the
effects of acceleration, and an etching process is required in
forming this gap. However, with respect to the semiconductor
acceleration sensor chip 10 of this embodiment, since the under
surface of the fixed portion 11 and the under surface of the
plummet portion 12 are formed at approximately the same height,
there is no need for such etching process in order to form the
gap.
[0031] The plummet portion 12 and the fixed portion 11 are
separated by a gap 14. In an approximate central portion of each
edge of the fixed portion 11 and the plummet portion 12, the gap 14
has a spacing of about 0.3 mm between the fixed portion 11 and the
plummet portion 12, for instance, and this spacing of the gap 14 is
set wider than the structure of the conventional semiconductor
acceleration sensor chip. Thereby, it is possible to prevent
possible foreign substance, such as chips that have fallen during
the dicing process etc., from entering into the gap and disturbing
the operation of the acceleration sensor.
[0032] The beam portions 13 are plate portions or thin portions of
the semiconductor substrate, and they connect the fixed portion 11
and the plummet portion 12. The beam portions 13 are formed such
that each beam portion 13 connects each diagonal points of the
fixed portion 11 and the plummet portion 12, and they are formed to
have flexibility so that they will bend in response to the vertical
and horizontal movements of the plummet portion 12. On the upper
surface of each beam portion 13, a plurality of piezo elements 16
are formed at predetermined intervals. The piezo elements 16 will
have their resistance values changed as the beam portions 13 bend
in the vertical and horizontal directions by the act of
acceleration. Signals based on the changes of resistance values of
the piezo elements 16 are taken out to the outside by wirings (not
shown) through the electrode pads 15. According to this embodiment,
since the semiconductor acceleration sensor chip 10 has a structure
in which the plummet portion 12 is located in the periphery of the
semiconductor acceleration sensor chip 10, it is possible to set
the area of the plummet portion 12 to be large, as mentioned above.
Accordingly, it is possible to acquire a desirable level of
sensitivity in the acceleration sensor without having to reduce the
thickness of the beam portions 13. Furthermore, by disposing the
beam portions 13 in the diagonal directions of the fixed portion 11
and the plummet portion 12, it is possible to set the length of the
beam portions 13 to be long, and thereby it is possible to improve
the sensitivity of the acceleration sensor even more.
[0033] The case 50 is formed using a ceramic, for instance, and it
has a bottom face portion 51 and a side portion 52.
[0034] The bottom face portion 51 has a projection portion 51a at
its central portion, and the outer shape of the projection portion
51a when viewed from above is an approximate square. The
semiconductor acceleration sensor chip 10 is supported by and fixed
to the bottom face portion 51 via the upper surface of the
projection portion 51a. The fixation of the semiconductor
acceleration sensor chip 10 to the upper surface of the projection
portion 51a is done, for example, by hardening a thermosetting
resin such as epoxy resin, silicon resin etc., by a heat treatment
at 150.degree. C. for 1 hour. The height of the projection portion
51a is 30 .mu.m, for instance, and the height of the fixed portion
11 of the semiconductor acceleration sensor chip 10 can be made
effectively higher than the plummet portion 12 by as much as the
height of the projection portion 51a. Due to such arrangement,
without touching the bottom face portion 51, the plummet portion 12
is able to move freely in response to the act of acceleration. For
instance, the projection portion 51a can be formed when
manufacturing the case 50 made of ceramic, by attaching an
approximately square green sheet, which is supposed to become the
projection portion 51a, to the surface of a portion of ceramic
material, i.e. the surface of a green sheet, which is supposed to
become the bottom face portion 51, and then sinter the square green
sheet. As to a manufactured case which does not have the projection
portion 51a, it is possible to form the projection portion 51a by
attaching an approximately square resin film (e.g. epoxy film)
during the mounting process of the semiconductor acceleration
sensor chip 10.
[0035] The side portion 52 is a sidewall of the case 50 which is
formed to be integrated with the bottom face portion 51. In the
central portion of each of the four sides of the side portion 52, a
plurality of wiring holes are formed, and external wiring
electrodes 53 leading to the exterior of the case 50 are disposed
at predetermined intervals so as to pass through these wiring
holes. The electrode pads 15 of the semiconductor acceleration
sensor chip 10 and the external wiring electrodes 53 are
electrically connected by bonding wires 54. In this case, for
instance, wire bonding is done by using gold wires as materials,
and by an ultrasonic concomitant thermocompression bonding method
at a temperature of 230.degree. C. In the semiconductor
acceleration sensor chip 10 of this embodiment, since the electrode
pads 15 are disposed on the surface of the fixed portion 11 which
is supported and fixed by the projection portion 51a, the
semiconductor acceleration sensor chip 10, especially the beam
portions 13, will not be damaged in the wire bonding process for
connecting the electrode pads 15 and the external wiring electrodes
53.
[0036] On the upper portion of the case 50, a metal cover 55 is
attached. The cover 55 is made using 42 alloy, SUS (stainless
steel), etc. as a material, and it is attached on the side portion
52 of the case 50 using a thermosetting resin so that the case 50
is sealed. The interior of the case 50 is purged by an N.sub.2 gas
or a dry air.
[0037] According to the semiconductor acceleration sensor 100 of
the first embodiment of the present invention, the plummet portion
12 of the semiconductor acceleration sensor chip 10 is disposed in
the peripheral portion, and thereby it is possible to set the
volume of the plummet portion to be large. Therefore, even if the
semiconductor acceleration sensor chip 10 is made thinner,
sufficient moment of inertia will act. Accordingly, in addition to
making the semiconductor acceleration sensor chip 10 thinner, it is
even possible to make the overall structure of the semiconductor
acceleration sensor 100 thinner. Furthermore, since sufficient
moment of inertia should act, even if the beam portion 13 is formed
with such thickness that can ensure predetermined mechanical
intensity, it is possible to acquire sufficient sensitivity of the
acceleration sensor. Moreover, by ensuring the mechanical intensity
of the beam portions 13, it is possible to improve the
shock-resistance of the acceleration sensor, by which damage that
may be caused in the manufacturing process and a possible reduction
in the yield ratio can be prevented.
[0038] Furthermore, by disposing the beam portions 13 in the
diagonal directions of the fixed portion 11 and the plummet portion
12, it is possible to set the length of the beam portions 13 to be
long, and thereby it is possible to improve the sensitivity of the
acceleration sensor even more.
[0039] Furthermore, by setting the spacing of the gap 14 wide, it
is possible to prevent possible foreign substances that can be
produced in the manufacturing process from entering into the gap 14
and inducing defects in the operation of the acceleration
sensor.
[0040] Furthermore, by having the structure in which the projection
portion 51a is formed on the bottom face portion 51 and the
semiconductor acceleration sensor chip 10 is supported by and fixed
to the upper surface of the projection portion 51a, it is possible
to have the under surface of the fixed portion 11 and the under
surface of the plummet portion 12 formed at approximately the same
height. Therefore, the manufacturing process of the semiconductor
acceleration sensor chip 10 can be simplified.
Second Embodiment
[0041] FIG. 2A and FIG. 2B are diagrams showing the structure of a
semiconductor acceleration sensor 200 according to a second
embodiment of the present invention. FIG. 2A is a plan view of the
semiconductor acceleration sensor 200 when it is viewed from above,
and FIG. 2B is a sectional view of the semiconductor acceleration
sensor 200 taken along a line A-A' shown in FIG. 2A. Note that for
convenience of explanation, FIG. 2A shows a state in which a cover
65, which is supposed to be placed on the upper surface of the
semiconductor acceleration sensor 200, is removed.
[0042] The semiconductor acceleration sensor 200 has a
semiconductor acceleration sensor chip 20 housed in a case 60 and
it is hermetically sealed by the cover 65.
[0043] The semiconductor acceleration sensor chip 20 is formed
using a silicon semiconductor substrate, for instance, and it has a
fixed portion 21, a plummet portion 22 and beam portions 23.
[0044] The fixed portion 21 is placed at a central portion of the
semiconductor acceleration sensor chip 20, and it has a circular
cylinder structure in which the shape thereof when viewed from
above is an approximate circle. A plurality of electrode pads 25
(which will be described later on) are disposed on the upper
surface of the fixed portion 21 at predetermined intervals. The
electrode pads 25 serve to take out signals from piezo elements 26
(which will be described later on) to the outside. The under
surface of the fixed portion 21 is fixed on a projection portion
61a which is formed on a bottom face portion 61 of the case 60
(which will be described later on).
[0045] Although the shape of the fixed portion 11 viewed from above
in the first embodiment is an approximate square, the shape of the
fixed portion 21 viewed from an above in this embodiment is an
approximate circle. The effect of this structure will be explained
using a comparative diagram shown in FIG. 3. If a length of one
side of the fixed portion 11 of which shape is an approximate
square is set to L, the length of the diagonal line will be set to
2.times.L. If the edge of the fixed portion 11 in which the shape
thereof when viewed from above is an approximate square contacts
with the edge of the fixed portion 21 in which the shape thereof
when viewed from above is an approximate circle, the length of the
diameter of the fixed portion 21 will be equal to the length of the
diagonal line of the fixed portion 11, i.e. 2.times.L. Therefore,
the area of the upper face of the fixed portion 11 becomes
L.times.L=L.sup.2, and the area of the upper face of the fixed
portion 21 becomes .pi..times.(1/
2).sup.2.times.L.sup.2=1.57.times.L.sup.2. It means that the area
of the upper face of the fixed portion 21 of which shape viewed
from above is an approximate circle is about 1.57 times the area of
the upper face of the fixed portion 11 in which the shape thereof
when viewed from above is an approximate square. Accordingly, the
bonded area between the semiconductor acceleration sensor chip 20
and the case 60 is larger than the first embodiment, and the
conjugation strength is improved.
[0046] The plummet portion 22 is a frame like portion shaped in an
approximate square, and it is located in a peripheral portion of
the semiconductor acceleration sensor chip 20 and formed in a way
which surrounds the fixed portion 21. By having the plummet portion
22 disposed in the peripheral portion of the semiconductor
acceleration sensor chip 20, it is possible to set the volume of
the plummet portion to be larger than the structure of the
conventional semiconductor sensor chip, i.e. the structure in which
the plummet portion is placed at a central portion of the
semiconductor acceleration sensor chip. Thereby, even if the
overall structure of the semiconductor acceleration sensor chip is
made thinner, a predetermined moment of inertia will act, and it
will be possible to prevent the sensitivity of the acceleration
sensor from deteriorating. Moreover, the under surface of the fixed
portion 21 and the under surface of the plummet portion 22 are
formed at approximately the same height. This means that the
manufacturing process of the semiconductor acceleration sensor chip
20 can be simplified. To be more precise, with respect to the
structure of the conventional semiconductor acceleration sensor
chip, a gap has to be formed between the under surface of the
plummet portion and the under surface of the fixed portion in order
to let the plummet portion displace more freely in response to the
effects of acceleration, and an etching process is required in
forming this gap. However, with respect to the semiconductor
acceleration sensor chip 20 of this embodiment, since the under
surface of the fixed portion 21 and the under surface of the
plummet portion 22 are formed at approximately same height, there
is no need for such etching process in order to form the gap.
[0047] The plummet portion 22 and the fixed portion 21 are
separated by a gap 24. The gap 24 is set wider than the structure
of the conventional semiconductor acceleration sensor chip.
Thereby, it is possible to prevent possible foreign substance, such
as chips that have fallen during the dicing process etc., from
entering into the gap and disturbing the operation of the
acceleration sensor.
[0048] The beam portions 23 are plate portions or thin portions of
the semiconductor substrate, and they connect the fixed portion 21
and the plummet portion 22. The beam portions 23 are formed such
that each beam portion 23 connects the fixed portion 21 and the
plummet portion 22 in each line which connects the diagonal points
of the plummet portion 22, and they are formed to have flexibility
so that they will bend in response to the vertical and horizontal
movements of the plummet portion 22. On the upper surface of each
beam portion 23, a plurality of piezo elements 26 are formed at
predetermined intervals. The piezo elements 26 will have their
resistance values changed as the beam portions 23 bend in the
vertical and horizontal directions by the act of acceleration.
Signals based on the changes of resistance values of the piezo
elements 26 are taken out to the outside by wirings (not shown)
through the electrode pads 25. According to this embodiment, since
the semiconductor acceleration sensor chip 20 has a structure in
which the plummet portion 22 is located in the peripheral of the
semiconductor acceleration sensor chip 20, it is possible to set
the area of the plummet portion 22 to be large, as mentioned above.
Accordingly, it is possible to acquire a desirable level of
sensitivity in the acceleration sensor without having to reduce the
thickness of the beam portions 23. Furthermore, by disposing the
beam portions 23 in the diagonal directions of the plummet portion
22, it is possible to set the length of the beam portions 23 to be
long, and thereby it is possible to improve the sensitivity of the
acceleration sensor even more.
[0049] The case 60 is formed using a ceramic, for instance, and it
has a bottom face portion 61 and a side portion 62.
[0050] The bottom face portion 61 has a projection portion 61a at
its central portion, and the outer shape of the projection portion
61a when viewed from above is an approximate circle. The
semiconductor acceleration sensor chip 20 is supported by and fixed
to the bottom face portion 61 via the upper surface of the
projection portion 61a. The fixation of the semiconductor
acceleration sensor chip 20 to the upper surface of the projection
portion 61a is done, for example, by hardening a thermosetting
resin such as epoxy resin, silicon resin etc., by a heat treatment
at 150.degree. C. for 1 hour. The height of the projection portion
61a is 30 .mu.m, for instance, and the height of the fixed portion
21 of the semiconductor acceleration sensor chip 20 can be made
effectively higher than the plummet portion 22 by as much as the
height of the projection portion 61a. Due to such arrangement,
without touching the bottom face portion 61, the plummet portion 22
is able to move freely in response to the act of acceleration. For
instance, the projection portion 61a can be formed when
manufacturing the case 60 made of ceramic, by attaching an
approximately circle green sheet, which is supposed to become the
projection portion 61a, to the surface of a portion of ceramic
material, i.e. the surface of a green sheet, which is supposed to
become the bottom face portion 61, and then sinter the circle green
sheet. As to a manufactured case which does not have the projection
portion 61a, it is possible to form the projection portion 61a by
attaching an approximately circle resin film (e.g. epoxy film)
during the mounting process of the semiconductor acceleration
sensor chip 20.
[0051] The side portion 62 is a sidewall of the case 60 which is
formed as being integrated with the bottom face portion 61. In the
central portion of each of the four sides of the side portion 62, a
plurality of wiring holes are formed, and external wiring
electrodes 63 leading to the exterior of the case 60 are disposed
at predetermined intervals so as to pass through these wiring
holes. The electrode pads 25 of the semiconductor acceleration
sensor chip 20 and the external wiring electrodes 63 are
electrically connected by bonding wires 64. In this case, for
instance, wire bonding is done by using gold wires as materials,
and by an ultrasonic concomitant thermocompression bonding method
at a temperature of 230.degree. C. In the semiconductor
acceleration sensor chip 20 of this embodiment, since the electrode
pads 25 are disposed on the surface of the fixed portion 21 which
is supported and fixed by the projection portion 61a, the
semiconductor acceleration sensor chip 20, especially the beam
portions 23 will not be damaged in the wire bonding process for
connecting the electrode pads 25 and the external wiring electrodes
63.
[0052] On the upper portion of the case 60, a metal cover 65 is
attached. The cover 65 is made using 42 alloy, SUS (stainless
steel) etc. as a material, and it is attached on the side portion
62 of the case 60 using a thermosetting resin so that the case 60
is sealed. The interior of the case 60 is purged by an N.sub.2 gas
or a dry air.
[0053] According to the semiconductor acceleration sensor 200 of
the second embodiment of the present invention, the same effects as
the semiconductor acceleration sensor 100 according to the first
embodiment of the present invention can be obtained. That is, the
plummet portion 22 of the semiconductor acceleration sensor chip 20
is disposed in the peripheral portion, and thereby it is possible
to set the volume of the plummet portion to be large. Therefore,
even if the semiconductor acceleration sensor chip 20 is made
thinner, sufficient moment of inertia will act. Accordingly, in
addition to making the semiconductor acceleration sensor chip 20
thinner, it is even possible to make the overall structure of the
semiconductor acceleration sensor 200 thinner. Furthermore, since
sufficient moment of inertia should act, even if the beam portion
23 is formed with such thickness that can ensure predetermined
mechanical intensity, it is possible to acquire sufficient
sensitivity of the acceleration sensor. Moreover, by ensuring the
mechanical intensity of he beam portions 23, it is possible to
improve the shock-resistance of the acceleration sensor, by which
damage that may be caused in the manufacturing process and a
possible reduction in the yield ratio can be prevented.
[0054] Furthermore, by disposing the beam portions 23 in the
diagonal directions of the plummet portion 22, it is possible to
set the length of the beam portions 23 to be long, and thereby it
is possible to improve the sensitivity of the acceleration sensor
even more.
[0055] Furthermore, by setting the spacing of the gap 24 wide, it
is possible to prevent possible foreign substances that can be
produced in the manufacturing process from entering into the gap 24
and inducing defects in the operation of the acceleration
sensor.
[0056] Furthermore, by having the structure in which the projection
portion 61a is formed on the bottom face portion 61 and the
semiconductor acceleration sensor chip 20 is supported by and fixed
to the upper surface of the projection portion 61a, it is possible
to have the under surface of the fixed portion 21 and the under
surface of the plummet portion 22 formed at approximately the same
height. Therefore, the manufacturing process of the semiconductor
acceleration sensor chip 20 can be simplified.
[0057] Moreover, according to the second embodiment of the present
invention, the fixed portion 21 of the semiconductor acceleration
sensor chip 20 has a circular cylinder structure in which the shape
thereof when viewed from above is an approximate circle. In this
structure, the bonded area between the semiconductor acceleration
sensor chip 20 and the case 60 is larger, and thereby the
conjugation strength is improved. Therefore, in this embodiment, in
addition to the above-mentioned effects, it is possible to further
improve the shock-resistance of the acceleration sensor.
Third Embodiment
[0058] FIG. 4A and FIG. 4B are diagrams showing the structure of a
semiconductor acceleration sensor 300 according to a third
embodiment of the present invention. FIG. 4A is a plan view of the
semiconductor acceleration sensor 300 when it is viewed from above,
and FIG. 4B is a sectional view of the semiconductor acceleration
sensor 300 taken along a line A-A' shown in FIG. 4A. Note that for
convenience of explanation, FIG. 4A shows a state in which a cover
75, which is supposed to be placed on the upper surface of the
semiconductor acceleration sensor 300, is removed.
[0059] The semiconductor acceleration sensor 300 has a structure in
which a semiconductor acceleration sensor chip 10 or 20 is mounted
on an integrated circuit 30 which controls the semiconductor
acceleration sensor chip 10 or 20, and is housed in a case 70
together with the integrated circuit 30 which is hermetically
sealed by the cover 75.
[0060] In this embodiment, both the semiconductor acceleration
sensor chip 10 according to the first embodiment and the
semiconductor acceleration sensor chip 20 according to the second
embodiment are applicable. In the following, a case where the
semiconductor acceleration sensor chip 10 is applied will be
described in order to make the following explanation simple. In
addition, in the following, the same reference numbers will be used
for the structural elements that are the same as the semiconductor
acceleration sensor chip 10 in the first embodiment, and redundant
explanations of those structure elements will be omitted.
[0061] The integrated circuit 30 is an IC for correcting
sensitivity and misalignment in the X, Y and Z axes. The under
surface of the integrated circuit 30 is fixed on a bottom face
portion 71 of the case 70 (which will be described later on). The
semiconductor acceleration sensor chip 10 is mounted on the upper
surface of the integrated circuit 30. The fixation of the
semiconductor acceleration sensor chip 10 to the upper surface of
the integrated circuit 30 is done, for instance, by hardening a
thermosetting resin such as epoxy resin, silicon resin etc., by a
heat treatment at 150.degree. C. for 1 hour. A plurality of
electrode pads 31 for transmitting signals between the integrated
circuit 30 and the semiconductor acceleration sensor chip 10 are
disposed on the upper surface of the integrated circuit 30 at
predetermined intervals. The electrode pads 31 are electrically
connected to several electrode pads 15 of the semiconductor
acceleration sensor chip 10 via bonding wires 32 which pass through
the gap 14. In this case, for instance, wire bonding is done by
using gold wires as materials, and by an ultrasonic concomitant
thermocompression bonding method at a temperature of 230.degree. C.
The integrated circuit 30 in this embodiment achieves structurally
the same function as the projection portion 51a of the case 50 in
the first embodiment. In other words, in this embodiment, the
height of the fixed portion 11 of the semiconductor acceleration
sensor chip 10 can be made effectively higher than the plummet
portion 12 by as much as the height of the integrated circuit 30.
Due to such arrangement, without touching the bottom face portion
71, the plummet portion 12 is able to move freely in response to
the act of acceleration.
[0062] The case 70 is formed using a ceramic, for instance, and it
has the bottom face portion 71 and a side portion 72.
[0063] The semiconductor acceleration sensor chip 10 is supported
by and fixed to the upper surface of the bottom face portion 71.
The fixation of the semiconductor acceleration sensor chip 10 to
the upper surface of the bottom face portion 71 is done, for
example, by hardening a thermosetting resin such as epoxy resin,
silicon resin etc., by a heat treatment at 150.degree. C. for 1
hour.
[0064] The side portion 72 is a sidewall of the case 70 which is
formed as being integrated with the bottom face portion 71. In the
central portion of each of the four sides of the side portion 72, a
plurality of wiring holes are formed, and external wiring
electrodes 73 leading to the exterior of the case 70 are disposed
at predetermined intervals so as to pass through these wiring
holes. The electrode pads 15 of the semiconductor acceleration
sensor chip 10 and the external wiring electrodes 73 are
electrically connected by bonding wires 74. In this case, for
instance, wire bonding is done by using gold wires as materials,
and by an ultrasonic concomitant thermocompression bonding method
at a temperature of 230.degree. C. In the semiconductor
acceleration sensor chip 10 of this embodiment, since the electrode
pads 15 are disposed on the surface of the fixed portion 11 which
is supported and fixed by the integrated circuit 30, the
semiconductor acceleration sensor chip 10, especially the beam
portions 13, will not be damaged in the wire bonding process for
connecting the electrode pads 15 and the external wiring electrodes
73.
[0065] On the upper portion of the case 70, a metal cover 75 is
attached. The cover 75 is made using 42 alloy, SUS (stainless
steel), etc. as a material, and it is attached on the side portion
72 of the case 70 using a thermosetting resin so that the case 70
is sealed. The interior of the case 70 is purged by an N.sub.2 gas
or a dry air.
[0066] According to the semiconductor acceleration sensor 300 of
the third embodiment of the present invention, the plummet portion
12 (22) of the semiconductor acceleration sensor chip 10 (20) is
disposed in the peripheral portion, and thereby it is possible to
set the volume of the plummet portion to be large. Therefore, even
if the semiconductor acceleration sensor chip 10 (20) is made
thinner, sufficient moment of inertia will act. Accordingly, it is
possible to make the semiconductor acceleration sensor chip 10 (20)
thinner. Furthermore, since sufficient moment of inertia should
act, even if the beam portion 13 (23) is formed with such thickness
that can ensure predetermined mechanical intensity, it is possible
to acquire sufficient sensitivity of the acceleration sensor.
Moreover, by ensuring the mechanical intensity of the beam portions
13 (23), it is possible to improve the shock-resistance of the
acceleration sensor, by which damage that may be caused in the
manufacturing process and a possible reduction in the yield ratio
can be prevented.
[0067] Furthermore, by disposing the beam portions 13 (23) in the
diagonal directions of the plummet portion 12 (22), it is possible
to set the length of the beam portions 13 (23) to be long, and
thereby it is possible to improve the sensitivity of the
acceleration sensor even more.
[0068] Furthermore, by setting the spacing of the gap 14 (24) wide,
it is possible to prevent possible foreign substances that can be
produced in the manufacturing process from entering into the gap 14
(24) and inducing defects in the operation of the acceleration
sensor.
[0069] Furthermore, by having the structure in which the integrated
circuit 30 is disposed between the bottom face portion 71 and the
semiconductor acceleration sensor chip 10 (20) and the
semiconductor acceleration sensor chip 10 (20) is supported by and
fixed to the upper surface of the integrated circuit 30, it is
possible to have the under surface of the fixed portion 11 (21) and
the under surface of the plummet portion 12 (22) formed at
approximately the same height. Therefore, the manufacturing process
of the semiconductor acceleration sensor chip 10 (20) can be
simplified.
[0070] Moreover, by having a structure in which the semiconductor
acceleration sensor chip 10 (20) is mounted on the integrated
circuit 30, it is possible to downsize the semiconductor
acceleration sensor 300 housing the integrated circuit 30 and the
semiconductor acceleration sensor chip 10 (20).
[0071] Moreover, by passing the bonding wires 32 which connect the
electrode pads 15 (25) of the semiconductor acceleration sensor
chip 10 (20) and the electrode pads 31 of the integrated circuit 30
with the bonding wires 32 through the gap 14, it is possible to
shorten the length of the bonding wires 32, and thus noise
resistance can be improved.
Fourth Embodiment
[0072] FIG. 5A and FIG. 5B are diagrams showing the structure of a
semiconductor acceleration sensor 400 according to a fourth
embodiment of the present invention. FIG. 5A is a plan view of the
semiconductor acceleration sensor 400 when it is viewed from above,
and FIG. 5B is a sectional view of the semiconductor acceleration
sensor 400 taken along a line A-A' shown in FIG. 5A. Note that for
convenience of explanation, FIG. 5A shows a state in which a cover
85, which is supposed to be placed on the upper surface of the
semiconductor acceleration sensor 400, is removed.
[0073] The semiconductor acceleration sensor 400 has a structure in
which the semiconductor acceleration sensor chip 10 or 20 and an
integrated circuit 40 which are arranged side-by-side are housed in
a case 80, which is hermetically sealed by the cover 85.
[0074] In this embodiment, both of the semiconductor acceleration
sensor chip 10 according to the first embodiment and the
semiconductor acceleration sensor chip 20 according to the second
embodiment are applicable. In the following, a case where the
semiconductor acceleration sensor chip 10 is applied will be
described in order to make the following explanation simple. In
addition, in the following, the same reference numbers will be used
for the structural elements that are the same as the semiconductor
acceleration sensor chip 10 in the first embodiment, and redundant
explanations of those structure elements will be omitted.
[0075] The integrated circuit 40 is an IC for correcting
sensitivity and misalignment in the X, Y and Z axes. The integrated
circuit 40 is arranged side-by-side with the semiconductor
acceleration sensor chip 10. The under surface of the integrated
circuit 40 is fixed on a bottom face portion 81 of the case 80
(which will be described later on). A plurality of electrode pads
41 for transmitting signals between the integrated circuit 40 and
the semiconductor acceleration sensor chip 10 and between the
integrated circuit 40 and external circuits are disposed on the
upper surface of the integrated circuit 40 at predetermined
intervals. The electrode pads 41 are electrically connected to
several electrode pads 15 of the semiconductor acceleration sensor
chip 10 and external wiring electrodes 83 via bonding wires 42. In
this case, for instance, wire bonding is done by using gold wires
as materials, and by an ultrasonic concomitant thermocompression
bonding method at a temperature of 230.degree. C.
[0076] The case 80 is formed using a ceramic, for instance, and it
has the bottom face portion 81 and a side portion 82.
[0077] The bottom face portion 81 has a projection portion 81a at
its central portion, and the outer shape of the projection portion
81a when viewed from above is an approximate square. The
semiconductor acceleration sensor chip 10 is supported by and fixed
to the bottom face portion 81 via the upper surface of the
projection portion 81a. The fixation of the semiconductor
acceleration sensor chip 10 to the upper surface of the projection
portion 81a is done, for example, by hardening a thermosetting
resin such as epoxy resin, silicon resin etc., by a heat treatment
at 150.degree. C. for 1 hour. The height of the projection portion
81a is 30 .mu.m, for instance, and the height of the fixed portion
11 of the semiconductor acceleration sensor chip 10 can be made
effectively higher than the plummet portion 12 by as much as the
height of the projection portion 81a. Due to such arrangement,
without touching the bottom face portion 81, the plummet portion 12
is able to move freely in response to the act of acceleration. For
instance, the projection portion 81a can be formed when
manufacturing the case 80 made of ceramic, by attaching an
approximately square green sheet, which is supposed to become the
projection portion 81a, to the surface of a portion of ceramic
material, i.e. the surface of a green sheet, which is supposed to
become the bottom face portion 81, and then sinter the square green
sheet. As to a manufactured case which does not have the projection
portion 81a, it is possible to form the projection portion 81a by
attaching an approximately square resin film (e.g. epoxy film) at
the mounting process of the semiconductor acceleration sensor chip
10.
[0078] The side portion 82 is a sidewall of the case 80 which is
formed as being integrated with the bottom face portion 81. In the
central portion of each of the four sides of the side portion 82, a
plurality of wiring holes are formed, and external wiring
electrodes 83 leading to the exterior of the case 80 are disposed
at predetermined intervals so as to pass through these wiring
holes. The electrode pads 15 of the semiconductor acceleration
sensor chip 10 and the external wiring electrodes 83 are
electrically connected by bonding wires 84. The electrode pads 41
of the integrated circuit 40 and the external wiring electrodes 83
are electrically connected by bonding wires 42. In this case, for
instance, wire bonding is done by using gold wires as materials,
and by an ultrasonic concomitant thermocompression bonding method
at a temperature of 230.degree. C. In the semiconductor
acceleration sensor chip 10 of this embodiment, since the electrode
pads 15 are disposed on the surface of the fixed portion 11 which
is supported and fixed by the projection portion 81a, the
semiconductor acceleration sensor chip 10, especially the beam
portions 13 will not be damaged in the wire bonding process for
connecting the electrode pads 15 and the external wiring electrodes
83.
[0079] On the upper portion of the case 80, a metal cover 85 is
attached. The cover 85 is made using 42 alloy, SUS (stainless
steel) etc. as a material, and it is attached on the side portion
82 of the case 80 using a thermosetting resin so that the case 80
is sealed. The interior of the case 80 is purged by an N.sub.2 gas
or a dry air.
[0080] According to the semiconductor acceleration sensor 400 of
the fourth embodiment of the present invention, the plummet portion
12 (22) of the semiconductor acceleration sensor chip 10 (20) is
disposed in the peripheral portion, and thereby it is possible to
set the volume of the plummet portion to be large. Therefore, even
if the semiconductor acceleration sensor chip 10 (20) is made
thinner, sufficient moment of inertia will act. Accordingly, it is
possible to make the semiconductor acceleration sensor chip 10 (20)
thinner. Furthermore, since sufficient moment of inertia should
act, even if the beam portion 13 (23) is formed with such thickness
that can ensure predetermined mechanical intensity, it is possible
to acquire sufficient sensitivity of the acceleration sensor.
Moreover, by ensuring the mechanical intensity of the beam portions
13 (23), it is possible to improve the shock-resistance of the
acceleration sensor, by which damage that may be caused in the
manufacturing process and a possible reduction in the yield ratio
can be prevented.
[0081] Furthermore, by disposing the beam portions 13 (23) in the
diagonal directions of the plummet portion 12 (22), it is possible
to set the length of the beam portions 13 (23) to be long, and
thereby it is possible to improve the sensitivity of the
acceleration sensor even more.
[0082] Furthermore, by setting the spacing of the gap 14 (24) wide,
it is possible to prevent possible foreign substances that can be
produced in the manufacturing process from entering into the gap 14
(24) and inducing defects in the operation of the acceleration
sensor.
[0083] Furthermore, by having the structure in which the projection
portion 81a is formed on the bottom face portion 81 and the
semiconductor acceleration sensor chip 10 (20) is supported by and
fixed to the upper surface of the projection portion 81a, it is
possible to have the under surface of the fixed portion 11 (21) and
the under surface of the plummet portion 12 (22) formed at
approximately same height. Therefore, the manufacturing process of
the semiconductor acceleration sensor chip 10 (20) can be
simplified.
[0084] Moreover, by having a structure in which the semiconductor
acceleration sensor chip 10 (20) and the integrated circuit 40 are
arranged side-by-side, it is possible to make the overall structure
of the semiconductor acceleration sensor 400 thinner.
[0085] This application claims priority to Japanese Patent
Application No. 2004-367933. The entire disclosures of Japanese
Patent Application No. 2004-367933 is hereby incorporated herein by
reference.
[0086] While only selected embodiments have been chosen to
illustrate the present invention, it will be apparent to those
skilled in the art from this disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. Furthermore,
the foregoing descriptions of the embodiments according to the
present invention are provided for illustration only, and not for
the purpose of limiting the invention as defined by the appended
claims and their equivalents. Thus, the scope of the invention is
not limited to the disclosed embodiments.
[0087] The term "configured" as used herein to describe a
component, section or part of a device includes hardware and/or
software that is constructed and/or programmed to carry out the
desired function.
[0088] Moreover, terms that are expressed as "means-plus function"
in the claims should include any structure that can be utilized to
carry out the function of that part of the present invention.
[0089] The terms of degree such as "substantially," "about," and
"approximately" as used herein mean a reasonable amount of
deviation of the modified term such that the end result is not
significantly changed. For example, these terms can be construed as
including a deviation of at least .+-.5% of the modified term if
this deviation would not negate the meaning of the word it
modifies.
[0090] In the present application, some aspects of the present
invention as described above are not stated in the claims, but they
are obvious aspects of the present invention and may be claimed in
another application. These aspects include the following.
[0091] In accordance with a first aspect of the present invention,
an acceleration sensor comprises a semiconductor acceleration
sensor chip, an integrated circuit and a case. The semiconductor
acceleration sensor chip has a fixed portion, a plummet portion
surrounding the fixed portion without contacting the fixed portion,
and a beam portion connecting the fixed portion and the plummet
portion. The thickness of the beam portion is thinner than the
thickness of the fixed portion. The integrated circuit is fixed to
the bottom face of the semiconductor acceleration sensor chip. The
case has a cavity housing the semiconductor acceleration sensor
chip and the integrated circuit. The bottom face of the integrated
circuit is fixed to the bottom face of the cavity of the case.
[0092] In accordance with a second aspect of the present invention,
in the acceleration sensor according to the first aspect of the
present invention, the shape of the plummet portion is an
approximately square column which has a cavity for housing the
fixed portion in the center thereof, and the beam portion connects
the plummet portion and the fixed portion on the diagonal line of
the cavity of the plummet portion.
[0093] In accordance with a third aspect of the present invention,
the acceleration sensor according to the second aspect of the
present invention further comprises first electrodes formed on the
surface of the fixed portion at predetermined intervals.
[0094] In accordance with a fourth aspect of the present invention,
the acceleration sensor according to the third aspect of the
present invention further comprises second electrodes formed on the
surface of the integrated circuit at predetermined intervals.
[0095] In accordance with a fifth aspect of the present invention,
the acceleration sensor according to the fourth aspect of the
present invention further comprises bonding wires electrically
connecting the first electrodes and the second electrodes through a
space between the fixed portion and the plummet portion.
[0096] In accordance with a sixth aspect of the present invention,
in the acceleration sensor according to the fifth aspect of the
present invention, the bonding wire is a gold wire and bonded to
the first electrode and the second electrode by means of an
ultrasonic concomitant thermocompression bonding method.
[0097] In accordance with a seventh aspect of the present
invention, the acceleration sensor according to the fifth aspect of
the present invention further comprises external wiring electrodes
formed at one or more side faces of the case, the external wiring
electrodes being electrically led to the exterior of the case; and
bonding wires electrically connecting the first electrodes and the
external wiring electrodes.
[0098] In accordance with an eighth aspect of the present
invention, in the acceleration sensor according to the seventh
aspect of the present invention, the bonding wire is a gold wire
and bonded to the first electrode and the external wiring electrode
by means of an ultrasonic concomitant thermocompression bonding
method.
[0099] In accordance with a ninth aspect of the present invention,
in the acceleration sensor according to the seventh aspect of the
present invention, the shape of the fixed portion is an
approximately square column.
[0100] In accordance with a tenth aspect of the present invention,
in the acceleration sensor according to the seventh aspect of the
present invention, the shape of the fixed portion is an
approximately circular cylinder.
* * * * *